Polymer electrolyte fuel cells (hereafter referred to as “PEFCs”) using hydrogen as fuel are being developed. In particular, a wide variety of PEFCs for automobiles and household power generation are being developed. Fuel cell systems for household power generation have been already commercialized. It is expected that fuel cell vehicles including fuel cells will also be commercialized in the near future. Unlike fuel cell systems for household power generation, the widespread use of fuel cell vehicles requires constructing a fuel supply infrastructure. That is, with the spread of the use of fuel cell vehicles, a hydrogen station has to be constructed in each region.
A hydrogen station stores high-purity, high-pressure hydrogen and supplies it to fuel cell vehicles. Methods for supplying fuel to a hydrogen station include a method of transporting hydrogen produced in a different place using a tank truck and a method of producing hydrogen at the hydrogen station. However, hydrogen has a low energy density and therefore is not suitable for transportation using a tank truck, unlike gasoline. For this reason, it is preferred to produce hydrogen, and purify and compress it at the hydrogen station. Also, it is predicted that small, low-cost hydrogen stations will be needed at the beginning of the widespread use of fuel cell vehicles.
As a hydrogen production process, there has been known a process that reforms town gas containing methane as a main component into hydrogen-containing reformed gas, purifies the reformed gas using a pressure swing adsorption (PSA) system, and compresses the resulting hydrogen using a compressor. However, a PSA system is large and costly. Further, the proportion of the reformed gas which can be recovered as high-purity hydrogen is typically 80% or less, and the remainder is used as the heat source of the reforming reaction. Furthermore, while compressing hydrogen to 700 to 1000 atmospheres, which are required by a hydrogen station, requires using a two-stage compressor system, such a compressor system has a low compression efficiency of 60 to 70%, wastes electrical energy, and is costly.
That is, the conventional hydrogen production process is disadvantageously large, costly, and low in energy conversion efficiency.
For this reason, there have been developed small, low-cost hydrogen production processes that simultaneously purify and compress hydrogen. As an example of such a process, Patent Literature 1 discloses a hydrogen compression process that purifies and compresses hydrogen-containing reformed gas. This process produces purified and compressed hydrogen on the cathode side from reformed gas supplied to the anode side by applying external electricity to the cell of a PEFC. This process is efficient and low-cost because it purifies and compresses hydrogen simultaneously and directly uses electrical energy as energy for purifying and compressing hydrogen.
Patent Literature 2 discloses a water electrolysis process that produces and compresses hydrogen by the electrolysis of water. This process produces compressed hydrogen on the cathode side by applying external electricity to the cell of a PEFC and thus electrolyzing water supplied to the anode side.